This invention relates to a sole plate for an ironing device which is made of a metal of high thermal conductivity, preferably aluminum, and has on its ironing side a coating of a mechanically resistant compound, preferably metallic or ceramic materials.
A sole plate of the type referred to above is described in prior U.S. patent application Ser. No. 06/759,406, Pat. No. 4,665,637. In order to reduce the weight of the ironing device making it easier to handle and to improve the thermal conductivity of the sole plate, a sole plate made of aluminum is used. In view of the reduced weight of the aluminum sole plate as compared with conventional materials such as iron or steel, the sliding ability of the sole plate over the article being ironed is improved.
Since aluminum is known to be less strong than iron or steel, ironing over hard objects as, for example, zippers or buttons tends to scratch the fabric contacting surface, causing burrs protruding from the face of the sole plate similar to a metal-cutting operation. When ironing particularly delicate textile fabrics such as silk, these burrs tend to pull threads from the fabric, thereby damaging it. However, such fabrics will be damaged already when such a burr merely roughens the silky lustrousness of the surface.
To avoid these disadvantages, in the patent application initially referred to the surface of the ironing side was coated with a mechanically resistant compound preferably composed of metallic or ceramic materials, applying flame or plasma spraying techniques. The mechanically resistant layer produced by spraying in this prior application has the disadvantage of being porous and of absorbing in particular water, humidity, air and other impurities which may penetrate to the aluminum sole plate. This produces corrosion on the aluminum surface on the ironing side, tending to cause warpage or blistering and even detachment of the mechanically resistant layer. In consequence thereof, the ironing side of the sole plate is damaged, damaging in turn the textile fabric being ironed in addition to requiring increased forces when moving the ironing device over the article being ironed.
In prolonged use, such sole plates known from the prior art are subject to a great deal of contamination by adhering fabric finishing agents, starch and textile particles burning into the surface when the ironing temperature is too high for these textiles. The result is a dull sole surface impairing the sliding ability over the article being ironed. Removing burnt-in finishing agents by cleaning agents is practically impossible. The only way to restore the sliding ability of the sole plate is to grind off the coating and apply a new coating to the sole plate.
From German published patent application DE-A1-1,952,846, it is further known to coat the metallic ironing side with a layer of temperature-resistant plastic material as, for example, PTFE, which resists contamination and has particularly good sliding abilities. Sole plates of this type in which the fabric contacting surfaces ar made of plastic material tend to become scratched easily and have an insufficient thermal stability, particularly when in continuous use or overheated. Particularly the plastic material becomes locally worn down completely by the pressing action. The scratch resistance is materially reduced particularly in sole plates made of aluminum since the hardness of the aluminum base is insufficient. It has been found that ironing over hard objects as, for example, metal zippers or buttons tends to produce deep scores extending into the aluminum surface, causing detachment of the plastic coating whereby the bare metal may become exposed. In the process, aluminum burrs form at the ends of the scratches which, protruding from the sole plate, eventually damage the article being ironed. Plastic burrs will form already when the plastic material has not yet been worn down to the metal surface.